In the case of measuring devices which implement a measurement of a broadband high-frequency signal in real-time in the time domain, the signal to be measured is very strongly influenced by the type and means of contacting of the device under test, for example, at a testing position, by means of a probe. In this context, a falsification of the actual characteristic curve of the measurement signal is caused by a plurality of effects, so that a measurement of the actually present signal becomes impossible.
Such measuring devices that measure the high-frequency signal in the time domain may comprise digital storage oscilloscopes. A deembedding, such as can be implemented with network analyzers, cannot be used in this form with measurements in the time domain because the mathematical operation corresponding to a multiplication in the frequency domain is a mathematical convolution operation in the time domain. Such convolution operations can only be realized with very large computational effort and can only be used on signals directed towards the past. Such computational operations cannot be used for a real-time analysis with broadband high-frequency signals.
Analyzing a high-frequency signal superposed with measurement errors in the time domain without the measurement errors having a significant influence on the presentation and analysis of the signal is therefore a general problem.
The publication EP 1 569 005 A2 proposes a calibration method in which a probe, which is provided for connecting a device under test to a measuring device, is fitted with a calibration unit. This calibration unit pre-distorts the high-frequency signal to be measured so that a subsequent distortion by the measuring device and the measurement cable is compensated. As a result of the complex mathematical operations, the calibration unit occupies a comparatively large volume and is therefore extremely unmanageable. An adaptation of such a probe for different devices under test is therefore possible only with difficulty. Beyond this, such a pre-distortion cannot completely compensate a measurement error.
Accordingly, there is a need for a measuring device and a method for operating the measuring device which can register and analyze a high-frequency signal reliably. Accordingly, any measurement errors which are superposed on the signal to be measured by the measurement setup can be reliably compensated.